The methods for supplying power to a vibration motor, a kind of reception sensor of a mobile communication terminal as an example of electrical equipment, include lead wire soldering, the direct soldering of a FPCB of a terminal and a FPCB land of a vibrating motor, a supply method using a connector, a supply method using a contact spring attached to a vibration motor.
FIG. 1 is a view schematically showing a bar type vibration motor with a contact spring mounted thereon according to the related art.
As shown in FIG. 1, in the supply method using a contact spring 10, when a vibration motor 20 with a contact spring mounted thereon is secured to a terminal structure, and a terminal PCB designed according to the location of the contact spring 10 is secured to the terminal structure, a PCB land connected to a terminal power source comes into contact with the contact spring 10, whereby the weight 30 of the vibration motor 20 is eccentrically rotated to generate vibration.
To ensure smooth power supply through a contact between the contact spring 10 and the PCB land of the terminal, the contact spring 10 has to maintain a proper level of repulsive force, and has to be designed so that the contact of the contact spring 10 may not deviate from the PCB land of the terminal.
FIG. 2 is a view showing a contact spring structure used for a vibration motor according to the related art.
Referring to (a) through (d) of FIG. 2, the related art contact spring 10 is of an integral type, roughly comprising a contact portion 11 contacting a PCB land connected to an external power source, a support portion 13 directly secured to the vibration motor or contacting the same, and a bent portion 12 connecting between the contact portion 11 and the support portion 13.
The contact portion 11 is basically formed in an arc-shaped curve in order to reduce the amount of change in the position of the contact with the PCB land of the terminal according to the amount of compression of the spring and increase the reliability of a connection between the PCB land and the contact, or may be embossed in the shape of a semispherical or arc-shaped strip.
The support portion 13 is constructed of a horizontal surface, a vertical surface, or a combination of a horizontal surface and a vertical surface, and may be constructed in various shapes according to the type of a vibration motor used or limiting conditions of instruments. Further, a soldering form for electrically connecting a coil end of the motor and the contact spring 10 may be added to the support portion 13, or alternatively they may be electrically connected by soldering or welding.
The bent portion 12 is basically constructed in a shape similar to a ‘⊂’ shape or its symmetrical shape, or may be constructed in a complete semispherical shape according to whether fillet treatment is done or not.
In the related art contact spring structure, most parts of the energy stored in the contact spring as the contact spring is compressed are concentrated on the bent portion 12, and the energy is proportional to the square of a strain.
At this time, the intensity of stress generated in the contact spring is proportional to the amount of strain by Hook's Law (stress=Young's modulus×strain). If a stress exceeding the threshold of the spring as represented by a tensile strength is generated, there may occur a phenomenon that the contact spring is permanently deformed.
In case of such a permanent deformation, there is a risk that the size of a repulsive force, generated when the contact between the PCB land of the terminal and the contact spring are compressed, may be reduced lower than a proper level, and thereby a power supply to the vibration motor is not done smoothly.
Moreover, the elastic modulus (k) of the spring is proportional to the thickness (T) of spring material and the surface area (A) of the bent portion, and the energy (E) stored in the bent portion is expressed as a function of the elastic modulus (k) and of the amount of compression (x). Further, the volume (V) of the bent portion is equal to the product of the thickness of spring material and the surface area (A).
In other words, in k∝T3A,
      E    =                  1        2            ⁢              kx        2              ,      V    =          T      ·      A        ,the energy (E/V) stored per unit volume of the spring is expressed by
      E    V    ⁢  α  ⁢      1    2    ⁢      r    2    ⁢      x    2  
As described above, while the energy density per unit volume represented by a strain-energy density is proportional to the square of a strain and of a spring thickness (T), it is almost not affected by the surface area (A).
To increase the elastic modulus while keeping a constant amount of compression in such a related art contact spring structure, a method of increasing the thickness of the material or increasing the width of the surface area of the bent portion may be employed.
However, the stress generated by an increase of the thickness of the spring material increases in proportion to the thickness (T), thus reducing the durability.
Further, because the contact of the contact portion rotates relative to the bent portion, which is a region where the stress is concentrated, the contact moves in a direction perpendicular to the compression direction and may deviate from the PCB land of the terminal. If the length of the bent portion is increased in order to prevent an increase of the stress, the rotation center of the contact becomes far from the contact to thereby increase the amount of movement of the contact in a direction perpendicular to the compression direction.